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Aviation History
1946
1946 - 1473.PDF
AUGUST IST, 1946 FLIGHT 107 Coupled Twin An Interesting French esign : Improved Single* Engined Performance ONE of the most obvious ways of obtainingmost of the possible advantages of atwin-engined layout in small aircraft sizes is that of gearing the two engines to a single airscrew. The necessary shafting, gear- ing and free-wheeling arrangements are clearly a likely source of difficulties, extra weight and possible expense, and designers have so far been somewhat deterred. Even so, the idea is still, it seems, worth serious con- sideration at least when planning certain classe? of aircraft. In pre-war days, it may be remembered, something of the kind was attempted in America by Menascos when they introduced the Unitwin,'which was virtually a couple of Menasco engines geared together and driving a common airscrew. With this layout, the designer had the advan- tages of a coupled twin, but these were somewhat over- shadowed by inevitable cooling and accessibility difficulties. Recently an interesting design has appeared from the French M.A.T.R.A. concern. This, the R-75, has been planned by M. Roger Robert, who was previously the chief designer of the Bernard Aircraft Company. In the R-75 the two Mathis 175 h.p. air-cooled Gr-7S are mounted in the wings in the normal way with extensions from the supports forming a twin-boom tail structure. Through a system of shafts, a bevel box and a free-wheel arrangement, The two 175 h.p. Mathis are mounted in the noses of the twin booms. the two engines drive a single pusher airscrew aft of thecentral nacelle. With this installation the air-cooled engines can be kept conveniently cool, while the centre of gravity problems in the conventional pusher design have been avoided. It is arranged as a four-seater, with luggage space in the nacelle below the gear box and airscrew shaft. Naturally enough, the aircraft has a tricycle undercarriage. The estimate performance figures of the R-75 provide an indication of the relative single-engined performance. With such a layout there is, of course, no difficulty about engine- failure directional control at any speed, and no losses in drag from the necessity of holding rudder against a dead engine. According to calculations, while the maximum speed at sea level is 218 m.p.h. with both engines in action, it is 155 m.p.h. with one of them throttled back. The respective rates of climb at sea level are 1,214 ft/min against 345 ft/min, while the ceilings are 18,oooft and 7,500ft. In addition to its unorthodox power layout the R-75 is also unusual from the control point of view. In order to obtain the advantages of full-span high-lift flaps, the tail plane is designed with a very high aspect ratio so that the two elevator surfaces can, at the same time, perform the duties of ailerons. These elevator-ailerons are normally operated through a fairly conventional control system, but the designer has planned the aircraft so that the rudders can be locked, leaving ->. two-control arrangement. M.A.T.R.A. will, incidentally, be showing the R-74—a single-engined version—at the Paris show in November. TvSo drawings which show the layout of the single-airscrew twin-engined R-75- FUTURE AUSTERS IN addition to the production of the 3-seater type developedfrom the Auster used during the war, and now named the Autocrat, Auster Aircraft are developing two more types. Thefirst, the VI, is a somewhat larger aircraft powered with a D.H. Gipsy Major and with " external " aerofoil flaps. Thesecond is the two-seater Auster Arrow, which has a 75 h.p. flat-four Continental. Ninety-five per cent of the Arrows are,we hear, earmarked for export. CONVERSION COURSES AIR SERVICE TRAINING, of Hamble, Southampton, havenow announced a schedule for their various ground con- version courses for ex-R.A.F. personnel. The assembly dates are:_ist Class Navigators' Licence, August 13th; 2nd ClassNavigators' Licence and "B" Licence Courses, August 20th and October 7th; Radio Officers' Conversion Courses, August13th, September 2nd and October ist; Radio Operators' Long Course, September 2nd and November ist; and Licensed Air-craft Engineering Course, September 24th. Incidentally, all the ground courses have been approved by the Ministry ofLabour and the Ministry of Education, under their training schemes.
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